1. Field of the Invention
The present invention relates to digital halftoning and, more particularly, to retaining high-frequency details and reducing visual artifacts in digitally-halftoned images.
2. Related Art
It is often desirable to reproduce a continuous-tone image, such as a black-and-white or color photograph, using an output device that is only capable of producing a discrete set of tones. For example, it has become increasingly desirable to reproduce continuous-tone images using bilevel output devices, such as laser printers and some types of thermal-transfer printers, that are only capable of printing black ink or toner on a page.
Discrete-tone output devices typically simulate continuous-tone images by producing a halftone of the continuous-tone image. Halftones use patterns of dots to simulate various tones. Such dot patterns tend to approximate the appearance of continuous tones when viewed by the human eye from a suitable distance.
With conventional halftoning techniques, there is typically a tradeoff between the spatial resolution (the number of pixels within a given area) and the intensity resolution (the number of tones that may be simulated) of the halftone. The higher the spatial resolution, the lower the intensity resolution, and vice versa. Furthermore, halftones may exhibit visual artifacts, such as Moiré patterns, that reduce the perceived quality of the halftone.
What is needed, therefore, are improved techniques for performing digital halftoning that preserve high-frequency details with less of an impact on intensity resolution than conventional halftoning techniques. What is also needed are techniques for reducing the appearance of visual artifacts in digital halftones.